Could vitamins do more harm than good? Experts advise that if you eat well, vitamins are unnecessary, and therefore a waste of money. Now, a new study holds that death rates are higher for older women who take a daily vitamin supplement than for those who don’t bother with vitamins.

The study, published in the Archives of Internal Medicine, shows an increased risk of death in older women who dutifully take a multivitamin, vitamin B6, folic acid, iron, magnesium, zinc, or copper supplement each day. Many older women take these substances in the hopes of preventing chronic disease, but over the years, women who took these vitamins and supplements were actually more likely to die of cardiovascular disease, cancer, and other causes. (Calcium supplements, by contrast, were seen to reduce the risk of death.)

“I think the main message is researchers are finding very little benefit from these substances,” says lead author Jaakko Murso, a nutritional epidemiologist at the University of Minnesota in Minneapolis. “Other studies have not shown the mortality risk our study shows, but those studies have not seen any positive effect either.”

So vitamins and dietary supplements may kill you, and they often provide little or no health benefit. That’s pretty shocking considering that about half of Americans take multivitamins regularly, and that vitamin and dietary supplement sales total over $20 billion annually in the U.S.

One doctor, when discussing how concerned parents are prone to going overboard giving their children unnecessary vitamins and supplements, says that these substances wind up resulting in little more than “expensive urine.”

The moral is: Don’t simply assume you or someone you love needs to take daily vitamins or supplements. Don’t make decisions after quickly scanning pill bottle labels in the neighborhood drugstore. Instead, do what you know you’re supposed to do, and ask your doctor for advice.

Brad Tuttle is a reporter at TIME. Find him on Twitter at @bradrtuttle. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.